Cellulosic article



Patented Feb. 23, 1943 CELLULOSIC ARTICLE William D. R. Strauglm, Kenmore, N. Y., assignor to E. I. do Pontde Nemours & Company, Wilmlngton, Del., a corporation of Delaware N Drawing.

Application January 20, 1940,

Serial No. 314,845

7 Claims. (Cl. 106-168) This invention relate to cellulosic articles, especially softened regenerated cellulose film. More particularly it appertains' to the prevention of color in softened regenerated structures.

The manufacture of regenerated cellulose film in a continuous manner from viscose is disclosed in U. S. A, Patent No. 1,548,864 (Brandenberger).

This procedure in general involves continuous extrusion of a sheet of cellulose xanthate solution (viscose) through a narrow slot directly into a coagulating (and/or regenerating) bath. The extruded web is kept in this bath until it has acquired the mechanical strength necessary to withstand subsequent treatments.

After the web has become strong enough it is removed from the coagulating bath and passed through a converting bath which convert (regenerates) the cellulose xanthate in the web to cellulose. After leaving the converting bath, the web is subjected to a series of treatments such as washing, desulfuring, washing, bleaching (or dyeing, depending upon the use which is to be made of the product), and washing, preferably in the order named. These last mentioned treatments (like the coagulating and converting treatments) are conveniently carried out by passing the continuous web through vats containing the corresponding treating liquid.

It is customary to provide for softeningth cellulose web by passing it through a solution of softener after it leaves the last washing bath and before it is dried. Usually the cellulosic sheet material i dried by passing it over heated rolls. This eliminates most of the water, but not the softener therefrom.

The softener is incorporated in the regenerated cellulose product in order to obtain flexibility,

increased durability and other desirable properties. Numerous materials suitable for this purpose are known to the art. The one most commonly used is glycerol, but extensive use has been made of other hygroscopic polyhydroxy compounds, for example, diethylene glycol, sorbitol,

months, for example, films softened with nitrogen containing substances, such as the formic acid, hydrochloric acid and sulfamic acid addition products of the mono-, di-, and tri-ethanolamines, are particularly prone to show this discoloration in a short time. Frequently the product is in the consumers hands by the time the discoloration has become objectionable. As a consequence, the removal of the discoloration is not possible or practical, and it has been the practice to avoid using a large number of materials exhibiting excellent softening characteristics merely because the softened article would show discoloration in a short period of time.

This invention had for an object the prevention or elimination of discoloration in softened regenerated cellulose. Other objects were to produce softened cellulosic materials free from discoloration, and to produce non-fibrous, transparent, re-

generated cellulose film which would remain free from discoloration for long periods of time. A general advance in the art, and other objects which will appear hereinafter, are also contemplated.

It has now been found that color in regenerated cellulose products (or discoloration) may be avoided (prevented, inhibited, restrained, curbed, repressed, eliminated) by incorporating in the film containing a softener which causes discoloration of the film with age, a reducing agent containing sulfur. The invention will be further understood from a consideration of the following examples, in which the parts are given by weight.

Example I A viscose film was extruded into a coagulating and/or regenerating bath, and then passed through the variou processing baths described in U. S. A. Patent No. 1,548,864 (Brandenberger) At the end of this treatment, the film was clear and transparent and in a gel condition, that is, it contained a, large amount of associated water (approximately 300%-400% water based upon the cellulose present).

At this point it was passed through an aqueous bath containing 7.5% ethanolamine formate and 0.5% sodiuinsulfite, after which it was passed through squeeze rolls which removed superficial liquid. Subsequent passage through a drying chamber for the removal of water vapor reduced the water content of the film to approximately 6% (based on the cellulose). In this form it was wound upon rolls. The film so prepared was found to be completely free of color and not to develop any appreciable color, even after aging for a period of more than 22 days.

A film prepared similarly, but omitting the sodium sulflte, was found to exhibit a faint tinge of yellow upon drying, and to be decidedly yellow, almost approaching a brown color at the end of 1 day.

Example II Gel film prepared as in Example I, before drying was passed through an aqueous bath comprising 10% of ethanolamine sulfamate and 0.5% of sodium sulfite. After the removal of superficial liquid it was dried upon conventional drying apparatus (U. S. Patent No. 1,606,824 to Brandenberger). The film so prepared was found to be completely colorless and remained so for more than 43 days. A film similarly prepared, but omitting the sodium sulfite, had a yellowish tinge, making it unsalable at the end of one day.

Example III Regenerated cellulose film, prepared similarly to that of Example I in the gel state and just prior to drying, was passed through an aqueous bath comprising 7.5% of ethanolamine sulfamate and 0.3% of amino imino methane sulfoxylic acid and the superficial water removed. This film, after drying, was found to be completely free from color and to remain so for a period of more than 63 days.

Example I V The film like that of Example I was passed through an aqueous bath containing 10% of ethanolamine hydrochloride and 0.6% of magnesium sulfite. This produced a film, after removal of excess water, containing 6% water, approximately 20% of ethanolamine hydrochloride and approximately 1.2% of magnesium sulfite. This film was free from color and remained so for a period of more than 15 days.

Example V A film similar to that of Example I was passed through an aqueous bath comprising 10% of ethanolamine hydrochloride and 0.6% sodium sulfite. After drying, the film containing approximately 20% ethanolamine hydrochloride and approximately 1.2% sodium sulfite, was completely colorless and remained substantially colorless for a period of more than 15 days.

Example VI A film prepared according to Example I was passed through an aqueous bath of glycerol and 0.1% of amino-imino-methane-sulfoxylic acid. After drying, this film was found to be substantially colorless and remained so for a period of 9 days at 140 F.

A similar film softened with the same quantity of glycerol, but containing no inhibitor, exhibited a slight yellowish tinge after 2 days when exposed to the same temperature.

The invention contemplates as a base any cellulosic structure, particularly those of pellicular nature such as sheet, artificial straw, caps, bands and continuous tubes, such as may be obtained by the coagulation and/or regeneration from an aqueous cellulosic dispersion or aqueous alkaline cellulosic solution.

From a chemical standpoint, the invention contemplates regenerated cellulose or cellulosic pellicles such as may be obtained from the viscose process and the cuprammonium process. It also comprehends glycol cellulose, cellulose glycolic acid, alkyl cellulose, and lowly esterified and etherified cellulose substitution derivatives and cellulosic structures of similar character. In the more common cellulose derivatives only one ether or ester group is associated with several cellulose units.

Various types of paper, especially the glassine type, may be used as the base material.

Sheets of albuminous material including gelatin, casein and the like, are also advantageously processed according to the present invention.

It will be clear, therefore, that the specific description has been made in connection with regenerated cellulose merely as a matter of convenience, and it is to be understood that the scope of the invention is broad enough to include many other bases with equal applicability.

Compounds containing the radical in which a: is 0 or 1, such as: sodium sulfite Nil-(I) Na-0S=O sodium sulfoxylate 11ocLn-0 Na0] sodium hydrosulfite Na-o-s o NaO-=0 amino-imino-methane sulfoxylic acid NH2-C etc, constitute the preferred group of color stabilizers. Other members of this group which may be mentioned specifically are sulfurous acid, soluble salts of sulfurous acid (such as potassium sulfite, magnesium sulfite, etc.) and the acid salts of sulfurous acid. The group also includes the alkali metal and alkaline earth metal salts of amino-imino-methane-sulfoxylic acid and other soluble salts and esters of this acid. Sulfide reducing agents, effective as decoloricing agents, are not generally acceptable (particularly in uses such as wrapping tissue) because their odor, or the odor of hydrogen sulfide which they may release, is objectionable.

The soluble thiosulfates may be used.

In general the color inhibiting agent should be present in the softened regenerated cellulose film to the extent of 0. to 1.0% (based on the cellulose). Even more may be used, but usually there is no advantage for the greater amount.

In order to get the aforementioned concentration in the dried and softened film, it is generally necessary (or convenient) that the material be soluble in an aqueous bath, such as that used for the application of the softener, to the extent of at least 0.03%.

It is desirable that the softening agent and the color inhibiting agent be applied simultaneously to the base. This is conveniently and efficiently done from an aqueous solution or dispersion containing both materials. Such a solution (or aqueous dispersion) may be applied to the gel product during the process of manufacture, for example, before the structure has been dehydrated. A dry article may be rewetted and treated with a solution or dispersion when such a procedure is desirable for some particular reason.

The softener and color inhibitor may be applied by spraying as well as by passage of the base through a body of the liquid containing the same.

The greatest advantages in reducing coloration or extending the time after which coloration first appears, is most pronounced in connection with nitrogen containing softening agents, as previously indicated, but the inhibitors are effective and increase the utility of the product with all other Softeners, including formamide, carbamide, glycerol, diethylene glycol, and the like.

The cellulosic structures, as prepared according to the present invention, have the advantage of improved appearance both when prepared and after aging for long periods of time. The lack of color in wrapping material, for example, is highly desirable in order that the appearance of the article wrapped remain unchanged. As will be obvious, the development of color in the wrapper (with age) will lead a prospective customer to be suspicious concerning the age and condition of the contents of the package. This is true even though the discoloration of the wrapper took place in a brief interval of time, which brief interval, for example, is insuflicient to adversely affect the condition of the wrapped article.

The art has heretofore been restricted in its use of softening agents, being able to employ only those with which a minor degree of discoloration occurred over moderate periods of aging, The present invention therefore not only enables improved results to be obtained with the commonly employed softeners, but also extends the field of practical softeners. Therefore, by the practice of the present invention manufacturers are enabled to employ softening agents which may exhibit desirable properties, such as a greater degree of softening action (making possible the use of lower concentrations), flame proofing action (and hence improved durability of the softened article), and a cost lower than that of the commonly used softening agents, etc. Softeners heretofore impractical are now available for sheet wrapping material, packaging, and the like, in which discoloration or development of color is indicated as a great disadvantage.

As many apparently widely different embodiments of this invention may be made without departing from the spirit and scope thereof, it is to be understood that this invention is not limited to the specific embodiments thereof except as defined in the appended claims.

I claim:

1. An article comprising essentially desulfured and washed regenerated cellulose softened with alkylol amine acid addition product and containing, as a color inhibiting agent, a soluble salt reducing agent containing a radical from the group consisting of 0S and 2. Sheet wrapping material comprising essentially desulfured and washed regenerated cellulose softened with alkylol amine addition product and containing, as a color inhibiting agent, sodium sulfoxylate.

3. Desulfured regenerated cellulose sheet wrapping material softened with 10% (based on the weight of the cellulosic material) ethanol amine hydrochloride and containing, as a color inhibitor, 1.2% sodium sulfite.

4. Desulfured and regenerated cellulosic sheet wrapping material softened with material from the group consisting of an alkylol amine acid addition product, ethanol formamide and urea and containing, as a color inhibitor, a reducing agent which is an alkali metal salt of an acid containing the radical o i=o 5. Desulfured and regenerated cellulosic sheet wrapping material softened with ethanol amine acid addition product and containing, as a color inhibitor, a reducing agent which is an alkali metal salt of an acid containing the radical 6. Cast desulfured regenerated cellulosic film softened wtih alkylol amine addition product and comprising 0.1% to 1.0% sodium sulfite color stabilizing agent.

'7. Cast desulfured regenerated cellulosic film softened with alkylol amine addition product and comprising 0.1% to 1.0% sodium hydrosulfite color stabilizing agent.

WILLIAM D. R. STRAUGHN.

CERTIFICATE OF CORRECTION. Patent No. 2,511,910. February 25, 19 5.

WILLIAM D. R. STRAUGHN.

It is hereby certified that error appears in the printed specification of the above numbered patent requiring correction as follows: Page 5, sec- 0nd column, 1ine l9, claim 1, for "-O-S read -0-S line 50, cleim for "wtih" read -with--; and that the said Letters Patent should bmread with this correction therein that the same may conform to the record of the casein the Patent Office.

Signed. and sealed this 27th day of April, A- D. 1915.

.Henry Van Arsdale, (Seal) Acting Commissioner of Patents. 

